I got fed up with felts over the years (of course I only had the garden variety to work with- the harder model referenced might well work ust fine). I attach a small round patch of leather from an old pad to the Bis key cup and then place a pad of cork under the A key. Carefully sanded to the appropriate thickness it works perfectly and because of the large surface area I've never had an issue with losing adjustment even after decades. The leather pad probably is overkill but I don't like thunking in the action and that renders it as silent as a normal felt setup.